2/7/2014 12:35 AM PST

Rocky drank raw eggs for protein ... but Manny Pacquiáo takes things a step further ... 'cause TMZ sports has learned, the eggs he likes to eat are filled with UNBORN BABY DUCKLINGS.

It's true ... the boiled duck fetuses -- called Balut -- are all the rage in the champ's native Philippines. The little duckies are cooked ALIVE right before they hatch ... and are eaten out of the shell.

Pac-man was at a press conference for his upcoming Timothy Bradley fight in NYC today ... when we asked him if the popular Filipino snack tastes as nasty as it looks.